The present invention relates to a raster scan type display using a cathod ray tube(CRT).
With the growing popularity of a computer, various numbers of display dots have been used and deflection frequencies of a display have also become various. Then, a multi-scanning display which can display signals of the various deflection frequencies by a single apparatus is becoming popular.
In the multi-scanning display, however, since there are various numbers of scanning lines, it is difficult to select a vertical pitch of a shadow mask so that no moire phenomenon occurs. Consequently, various techniques of moire cancellation have been proposed.
As conventional techniques regarding the display of this kind in which the moire phenomenon is cancelled, there are Japanese Laid-open Patent Publication Nos. HEI 5-236290(1993), HEI 5-236291(1993), and the like.
In the conventional display, a series circuit of a resistor and a switch is connected in parallel to an S-shaped capacitor in a vertical deflection circuit. By opening and closing the switch at half-frequency of the vertical deflection frequency, a DC current is superposed to a vertical deflection current and a display position is oscillated. As a result, the moire phenomenon is reduced. However, No consideration has been given to noises on an image plane which are caused by the use of the switch in the prior art.